Systems And Methods For Non-Rigid Deformation Of Tissue For Virtual Navigation Of Interventional Tools

ABSTRACT

A method of modeling anatomic deformation comprises receiving a reference three dimensional model of a branched anatomical formation in a reference state. The method further comprises applying a three dimensional deformation field to the reference three dimensional model to create a deformed three dimensional model of a deformed state of the branched anatomical formation and dynamically displaying an image of the deformed three dimensional model of the deformed state of the branched anatomical formation.

FIELD

The present disclosure is directed to systems and methods for navigatinga patient anatomy to conduct a minimally invasive procedure, and moreparticularly to systems and methods for dynamically deforming ananatomical passageway model for display.

BACKGROUND

Minimally invasive medical techniques are intended to reduce the amountof tissue that is damaged during interventional procedures, therebyreducing patient recovery time, discomfort, and deleterious sideeffects. Such minimally invasive techniques may be performed throughnatural orifices in a patient anatomy or through one or more surgicalincisions. Through these natural orifices or incisions clinicians mayinsert interventional instruments (including surgical, diagnostic,therapeutic, or biopsy instruments) to reach a target tissue location.To reach the target tissue location, a minimally invasive interventionalinstrument may navigate natural or surgically created passageways inanatomical systems such as the lungs, the colon, the intestines, thekidneys, the heart, the circulatory system, or the like. Teleoperatedinterventional systems may be used to insert and position theinterventional instrument within the patient anatomy. During navigationof the interventional instrument, the anatomical passageways may deformdue to, for example, anatomical motion (e.g. cardiac motion, respirationmotion) or a force applied by the interventional instrument. Systems andmethods are needed to dynamically deform anatomical passageway modelsfor display to a user while navigating the actual patient anatomicalpassageways with the interventional instrument.

SUMMARY

The embodiments of the invention are summarized by the claims thatfollow the description.

In one embodiment, method of modeling anatomic deformation comprisesreceiving a reference three dimensional model of a branched anatomicalformation in a reference state. The method further comprises applying athree dimensional deformation field to the reference three dimensionalmodel to create a deformed three dimensional model of a deformed stateof the branched anatomical formation and dynamically displaying an imageof the deformed three dimensional model of the deformed state of thebranched anatomical formation.

In another embodiment, a processing system comprises a processor and amemory having computer readable instructions stored thereon. Thecomputer readable instructions, when executed by the processor, causethe system to receive a reference three dimensional model of a branchedanatomical formation in a reference state. The instructions whenexecuted by the processor also cause the system to apply a threedimensional deformation field to the reference three dimensional modelto create a deformed three dimensional model of a deformed state of thebranched anatomical formation. The instructions when executed by theprocessor also cause the system to dynamically display an image of thedeformed three dimensional model of the deformed state of the branchedanatomical formation.

Additional aspects, features, and advantages of the present disclosurewill become apparent from the following detailed description.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isemphasized that, in accordance with the standard practice in theindustry, various features are not drawn to scale. In fact, thedimensions of the various features may be arbitrarily increased orreduced for clarity of discussion. In addition, the present disclosuremay repeat reference numerals and/or letters in the various examples.This repetition is for the purpose of simplicity and clarity and doesnot in itself dictate a relationship between the various embodimentsand/or configurations discussed.

FIG. 1 is a telerobotic interventional system, in accordance with anembodiment of the present disclosure.

FIG. 2 illustrates an interventional instrument system utilizing aspectsof the present disclosure.

FIG. 3 illustrates a method for generating a dynamic display of a modelof anatomic passageways in a deformed state.

FIG. 4 illustrates a three dimensional volumetric representation ofanatomic passageways in a reference state.

FIG. 5 illustrates a skeletal tree based on the reference model of FIG.4.

FIG. 6 illustrates a geometric model based on the reference model ofFIG. 4.

FIG. 7 illustrates the measurement of deformation of the anatomicpassageways in a first state of deformation.

FIG. 8 illustrates the measurement of deformation of the anatomicpassageways in a second state of deformation.

FIG. 9 illustrates a skeletal tree based on a composite deformation ofthe anatomic passageways.

FIG. 10 illustrates a deformation field describing the deformation ofthe anatomic passageways.

FIG. 11 illustrates a three dimensional geometric model of the anatomicpassageways with the composite deformation.

FIG. 12 illustrates the three dimensional volumetric representation ofanatomic passageways of FIG. 4 rendered with the composite deformation.

FIG. 13 illustrates the deformed three dimensional volumetricrepresentation of anatomic passageways of FIG. 12 with theinterventional instrument.

FIG. 14 illustrates a method of mesh model deformation using a graphicalprocessing unit (GPU).

DETAILED DESCRIPTION

In the following detailed description of the aspects of the invention,numerous specific details are set forth in order to provide a thoroughunderstanding of the disclosed embodiments. However, it will be obviousto one skilled in the art that the embodiments of this disclosure may bepracticed without these specific details. In other instances well knownmethods, procedures, components, and circuits have not been described indetail so as not to unnecessarily obscure aspects of the embodiments ofthe invention. And, to avoid needless descriptive repetition, one ormore components or actions described in accordance with one illustrativeembodiment can be used or omitted as applicable from other illustrativeembodiments.

The embodiments below will describe various instruments and portions ofinstruments in terms of their state in three-dimensional space. As usedherein, the term “position” refers to the location of an object or aportion of an object in a three-dimensional space (e.g., three degreesof translational freedom along Cartesian X, Y, Z coordinates). As usedherein, the term “orientation” refers to the rotational placement of anobject or a portion of an object (three degrees of rotationalfreedom—e.g., roll, pitch, and yaw). As used herein, the term “pose”refers to the position of an object or a portion of an object in atleast one degree of translational freedom and to the orientation of thatobject or portion of the object in at least one degree of rotationalfreedom (up to six total degrees of freedom). As used herein, the term“shape” refers to a set of poses, positions, or orientations measuredalong an elongated object.

Referring to FIG. 1 of the drawings, a telerobotic interventional systemfor use in, for example, surgical, diagnostic, therapeutic, or biopsyprocedures, is generally indicated by the reference numeral 100. As willbe described, the telerobotic interventional systems of this disclosureare generally under the teleoperational control of a surgeon. However,for some procedures or sub-procedures, the telterobotic interventionalsystem may be under the partial or full control of a computer programmedto perform the procedure or sub-procedure. As shown in FIG. 1, thetelerobotic interventional system 100 generally includes a roboticassembly 102 mounted to or near an operating table O on which a patientP is positioned. An interventional instrument system 104 is operablycoupled to the robotic assembly 102. An operator input system 106 allowsa surgeon or other type of clinician S to view the surgical site and tocontrol the operation of the interventional instrument system 104.

The operator input system 106 may be located at a surgeon's consolewhich is usually located in the same room as operating table O. However,it should be understood that the surgeon S can be located in a differentroom or a completely different building from the patient P. Operatorinput system 106 generally includes one or more control device(s) forcontrolling the interventional instrument system 104. The controldevice(s) may include any number of a variety of input devices, such ashand grips, joysticks, trackballs, data gloves, trigger-guns,hand-operated controllers, voice recognition devices, touch screens,body motion or presence sensors, or the like. In some embodiments, thecontrol device(s) will be provided with the same degrees of freedom asthe interventional instruments of the robotic assembly to provide thesurgeon with telepresence, or the perception that the control device(s)are integral with the instruments so that the surgeon has a strong senseof directly controlling instruments. In other embodiments, the controldevice(s) may have more or fewer degrees of freedom than the associatedinterventional instruments and still provide the surgeon withtelepresence. In some embodiments, the control device(s) are manualinput devices which move with six degrees of freedom, and which may alsoinclude an actuatable handle for actuating instruments (for example, forclosing grasping jaws, applying an electrical potential to an electrode,delivering a medicinal treatment, or the like).

The robotic assembly 102 supports the interventional instrument system104 and may comprise a kinematic structure of one or more non-servocontrolled links (e.g., one or more links that may be manuallypositioned and locked in place, generally referred to as a set-upstructure) and a robotic manipulator. The robotic assembly 102 includesplurality of actuators (e.g., motors) that drive inputs on theinterventional instrument 104. These motors actively move in response tocommands from the control system (e.g., control system 112). The motorsinclude drive systems which when coupled to the interventionalinstrument 104 may advance the interventional instrument into anaturally or surgically created anatomical orifice and/or may move thedistal end of the interventional instrument in multiple degrees offreedom, which may include three degrees of linear motion (e.g., linearmotion along the X, Y, Z Cartesian axes) and three degrees of rotationalmotion (e.g., rotation about the X, Y, Z Cartesian axes). Additionally,the motors can be used to actuate an articulable end effector of theinstrument for grasping tissue in the jaws of a biopsy device or thelike.

The robotic interventional system 100 also includes a sensor system 108with one or more sub-systems for receiving information about theinstruments of the robotic assembly. Such sub-systems may include aposition sensor system (e.g., an electromagnetic (EM) sensor system); ashape sensor system for determining the position, orientation, speed,pose, and/or shape of the catheter tip and/or of one or more segmentsalong a flexible body of instrument 104; and/or a visualization systemfor capturing images from the distal end of the catheter system.

The robotic interventional system 100 also includes a display system 110for displaying an image of the surgical site and interventionalinstruments 104 generated by sub-systems of the sensor system 108. Thedisplay 110 and the operator input system 106 may be oriented so theoperator can control the interventional instrument system 104 and theoperator input system 106 as if viewing the workspace in substantiallytrue presence. True presence means that the displayed tissue imageappears to an operator as if the operator was physically present at theimage location and directly viewing the tissue from the perspective ofthe image.

Alternatively or additionally, display system 110 may present images ofthe surgical site recorded and/or modeled preoperatively orintra-operatively using imaging technology such as computerizedtomography (CT), magnetic resonance imaging (MRI), fluoroscopy,thermography, ultrasound, optical coherence tomography (OCT), thermalimaging, impedance imaging, laser imaging, nanotube X-ray imaging, orthe like. The presented preoperative or intra-operative images mayinclude two-dimensional, three-dimensional, or four-dimensional(including e.g., time based or velocity based information) images andmodels.

In some embodiments, the display system 110 may display a virtualvisualization image in which the actual location of the interventionalinstrument is registered (e.g., dynamically referenced) withpreoperative or concurrent images to present the surgeon with a virtualimage of the internal surgical site at the location of the tip of thesurgical instrument.

In other embodiments, the display system 110 may display a virtualvisualization image in which the actual location of the interventionalinstrument is registered with prior images (including preoperativelyrecorded images) or concurrent images to present the surgeon with avirtual image of an interventional instrument at the surgical site. Animage of a portion of the interventional instrument 104 may besuperimposed on the virtual image to assist the surgeon controlling theinterventional instrument.

The robotic interventional system 100 also includes a control system112. The control system 112 includes at least one memory and at leastone processor (not shown), and typically a plurality of processors, foreffecting control between the interventional instrument system 104, theoperator input system 106, the sensor system 108, and the display system110. The control system 112 also includes programmed instructions (e.g.,a computer-readable medium storing the instructions) to implement someor all of the methods described herein. While control system 112 isshown as a single block in the simplified schematic of FIG. 1, thesystem may comprise a number of data processing circuits with a portionof the processing optionally being performed on or adjacent the roboticassembly 102, a portion being performed at the operator input system106, and the like. Any of a wide variety of centralized or distributeddata processing architectures may be employed. Similarly, the programmedinstructions may be implemented as a number of separate programs orsubroutines, or they may be integrated into a number of other aspects ofthe robotic systems described herein. In one embodiment, control system112 supports wireless communication protocols such as Bluetooth, IrDA,HomeRF, IEEE 802.11, DECT, and Wireless Telemetry.

In some embodiments, control system 112 may include one or more servocontrollers to provide force and torque feedback from the interventionalinstrument system 104 to one or more corresponding servomotors for theoperator input system 106. The servo controller(s) may also transmitsignals instructing robotic assembly 102 to move the interventionalinstruments 104 which extend into an internal surgical site within thepatient body via openings in the body. Any suitable conventional orspecialized servo controller may be used. A servo controller may beseparate from, or integrated with, robotic assembly 102. In someembodiments, the servo controller and robotic assembly are provided aspart of a robotic arm cart positioned adjacent to the patient's body.

The control system 112 may further include a virtual visualizationsystem to provide navigation assistance to the interventionalinstruments 104. Virtual navigation using the virtual visualizationsystem is based upon reference to an acquired dataset associated withthe three dimensional structure of the anatomical passageways. Morespecifically, the virtual visualization system processes images of thesurgical site recorded and/or modeled using imaging technology such ascomputerized tomography (CT), magnetic resonance imaging (MRI),fluoroscopy, thermography, ultrasound, optical coherence tomography(OCT), thermal imaging, impedance imaging, laser imaging, nanotube X-rayimaging, or the like. Software is used to convert the recorded imagesinto a two dimensional or three dimensional model of a partial or anentire anatomical organ or anatomical region. The model describes thevarious locations and shapes of the passageways and their connectivity.The images used to generate the model may be recorded preoperatively orintra-operatively during a clinical procedure. In an alternativeembodiment, a virtual visualization system may use standard models(i.e., not patient specific) or hybrids of a standard model and patientspecific data. The model and any virtual images generated by the modelmay represent the static posture of a deformable anatomic region duringone or more phases of motion (e.g., during an inspiration/expirationcycle of a lung).

During a virtual navigation procedure, the sensor system 108 may be usedto compute an approximate location of the instrument with respect to thepatient anatomy. The location can be used to produce both macro-leveltracking images of the patient anatomy and virtual internal images ofthe patient anatomy. Various systems for using fiber optic sensors toregister and display an interventional implement together withpreoperatively recorded surgical images, such as those from a virtualvisualization system, are known. For example U.S. patent applicationSer. No. 13/107,562, filed May 13, 2011, disclosing, “Medical SystemProviding Dynamic Registration of a Model of an Anatomical Structure forImage-Guided Surgery,” which is incorporated by reference herein in itsentirety, discloses one such system.

The robotic interventional system 100 may further include optionaloperation and support systems (not shown) such as illumination systems,steering control systems, irrigation systems, and/or suction systems. Inalternative embodiments, the robotic system may include more than onerobotic assembly and/or more than one operator input system. The exactnumber of manipulator assemblies will depend on the surgical procedureand the space constraints within the operating room, among otherfactors. The operator input systems may be collocated, or they may bepositioned in separate locations. Multiple operator input systems allowmore than one operator to control one or more manipulator assemblies invarious combinations.

FIG. 2 illustrates an interventional instrument system 200 which may beused as the interventional instrument system 104 of roboticinterventional system 100. Alternatively, the interventional instrumentsystem 200 may be used for non-robotic exploratory procedures or inprocedures involving traditional manually operated interventionalinstruments, such as endoscopy.

The instrument system 200 includes a catheter system 202 coupled to aninstrument body 204. The catheter system 202 includes an elongatedflexible catheter body 216 having a proximal end 217 and a distal end ortip portion 218. In one embodiment, the flexible body 216 has anapproximately 3 mm outer diameter. Other flexible body outer diametersmay be larger or smaller. The catheter system 202 may optionally includea shape sensor 222 for determining the position, orientation, speed,pose, and/or shape of the catheter tip at distal end 218 and/or of oneor more segments 224 along the body 216. The entire length of the body216, between the distal end 218 and the proximal end 217 may beeffectively divided into the segments 224. If the instrument system 200is an interventional instrument system 104 of a robotic interventionalsystem 100, the shape sensor 222 may be a component of the sensor system108. If the instrument system 200 is manually operated or otherwise usedfor non-robotic procedures, the shape sensor 222 may be coupled to atracking system that interrogates the shape sensor and processes thereceived shape data.

The shape sensor system 222 may include an optical fiber aligned withthe flexible catheter body 216 (e.g., provided within an interiorchannel (not shown) or mounted externally). In one embodiment, theoptical fiber has a diameter of approximately 200 μm. In otherembodiments, the dimensions may be larger or smaller.

The optical fiber of the shape sensor system 222 forms a fiber opticbend sensor for determining the shape of the catheter system 202. In onealternative, optical fibers including Fiber Bragg Gratings (FBGs) areused to provide strain measurements in structures in one or moredimensions. Various systems and methods for monitoring the shape andrelative position of an optical fiber in three dimensions are describedin U.S. patent application Ser. No. 11/180,389, filed Jul. 13, 2005,disclosing “Fiber optic position and shape sensing device and methodrelating thereto;” U.S. Provisional Pat. App. No. 60/588,336, filed onJul. 16, 2004, disclosing “Fiber-optic shape and relative positionsensing;” and U.S. Pat. No. 6,389,187, filed on Jun. 17, 1998,disclosing “Optical Fibre Bend Sensor,” which are incorporated byreference herein in their entireties. In other alternatives, sensorsemploying other strain sensing techniques such as Rayleigh scattering,Raman scattering, Brillouin scattering, and Fluorescence scattering maybe suitable. In other alternative embodiments, the shape of the cathetermay be determined using other techniques. For example, if the history ofthe catheter's distal tip pose is stored for an interval of time that issmaller than the period for refreshing the navigation display or foralternating motion (e.g., inhalation and exhalation), the pose historycan be used to reconstruct the shape of the device over the interval oftime. As another example, historical pose, position, or orientation datamay be stored for a known point of an instrument along a cycle ofalternating motion, such as breathing. This stored data may be used todevelop shape information about the catheter. Alternatively, a series ofpositional sensors, such as EM sensors, positioned along the cathetercan be used for shape sensing. Alternatively, a history of data from apositional sensor, such as an EM sensor, on the instrument during aprocedure may be used to represent the shape of the instrument,particularly if an anatomical passageway is generally static.Alternatively, a wireless device with position or orientation controlledby an external magnetic field may be used for shape sensing. The historyof its position may be used to determine a shape for the navigatedpassageways.

In this embodiment, the optical fiber may include multiple cores withina single cladding. Each core may be single-mode with sufficient distanceand cladding separating the cores such that the light in each core doesnot interact significantly with the light carried in other cores. Inother embodiments, the number of cores may vary or each core may becontained in a separate optical fiber.

In some embodiments, an array of FBG's is provided within each core.Each FBG comprises a series of modulations of the core's refractiveindex so as to generate a spatial periodicity in the refraction index.The spacing may be chosen so that the partial reflections from eachindex change add coherently for a narrow band of wavelengths, andtherefore reflect only this narrow band of wavelengths while passingthrough a much broader band. During fabrication of the FBG's, themodulations are spaced by a known distance, thereby causing reflectionof a known band of wavelengths. However, when a strain is induced on thefiber core, the spacing of the modulations will change, depending on theamount of strain in the core. Alternatively, backscatter or otheroptical phenomena that vary with bending of the optical fiber can beused to determine strain within each core.

Thus, to measure strain, light is sent down the fiber, andcharacteristics of the returning light are measured. For example, FBG'sproduce a reflected wavelength that is a function of the strain on thefiber and its temperature. This FBG technology is commercially availablefrom a variety of sources, such as Smart Fibres Ltd. of Bracknell,England. Use of FBG technology in position sensors for robotic surgeryis described in U.S. Pat. No. 7,930,065, filed Jul. 20, 2006, disclosing“Robotic Surgery System Including Position Sensors Using Fiber BraggGratings,” which is incorporated by reference herein in its entirety.

When applied to a multicore fiber, bending of the optical fiber inducesstrain on the cores that can be measured by monitoring the wavelengthshifts in each core. By having two or more cores disposed off-axis inthe fiber, bending of the fiber induces different strains on each of thecores. These strains are a function of the local degree of bending ofthe fiber. For example, regions of the cores containing FBG's, iflocated at points where the fiber is bent, can thereby be used todetermine the amount of bending at those points. These data, combinedwith the known spacings of the FBG regions, can be used to reconstructthe shape of the fiber. Such a system has been described by LunaInnovations. Inc. of Blacksburg, Va.

As described, the optical fiber may be used to monitor the shape of atleast a portion of the catheter system 202. More specifically, lightpassing through the optical fiber is processed to detect the shape ofthe catheter system 202 and for utilizing that information to assist insurgical procedures. The sensor system (e.g. sensor system 108) mayinclude an interrogation system for generating and detecting the lightused for determining the shape of the catheter system 202. Thisinformation, in turn, can be used to determine other related variables,such as velocity and acceleration of the parts of an interventionalinstrument. The sensing may be limited only to the degrees of freedomthat are actuated by the robotic system, or may be applied to bothpassive (e.g., unactuated bending of the rigid members between joints)and active (e.g., actuated movement of the instrument) degrees offreedom.

The interventional instrument system may optionally include a positionsensor system 220. The position sensor system 220 may be anelectromagnetic (EM) sensor system that includes one or more conductivecoils that may be subjected to an externally generated electromagneticfield. Each coil of the EM sensor system 220 then produces an inducedelectrical signal having characteristics that depend on the position andorientation of the coil relative to the externally generatedelectromagnetic field. In one embodiment, the EM sensor system may beconfigured and positioned to measure six degrees of freedom, e.g., threeposition coordinates X, Y, Z and three orientation angles indicatingpitch, yaw, and roll of a base point or five degrees of freedom, e.g.,three position coordinates X, Y, Z and two orientation angles indicatingpitch and yaw of a base point. Further description of an EM sensorsystem is provided in U.S. Pat. No. 6,380,732, filed Aug. 11, 1999,disclosing “Six-Degree of Freedom Tracking System Having a PassiveTransponder on the Object Being Tracked,” which is incorporated byreference herein in its entirety.

The flexible catheter body 216 includes a channel sized and shaped toreceive an auxiliary tool 226. Auxiliary tools may include, for example,image capture probes, biopsy devices, laser ablation fibers, or othersurgical, diagnostic, or therapeutic tools. Auxiliary tools may includeend effectors having a single working member such as a scalpel, a blade,an optical fiber, or an electrode. Other end effectors may include apair or plurality of working members such as forceps, graspers,scissors, or clip appliers, for example. Examples of electricallyactivated end effectors include electrosurgical electrodes, transducers,sensors, and the like. In various embodiments, the auxiliary tool 226may be an image capture probe including a distal portion with astereoscopic or monoscopic camera disposed near the distal end 218 ofthe flexible catheter body 216 for capturing images (including videoimages) that are processed for display. The image capture probe mayinclude a cable coupled to the camera for transmitting the capturedimage data. Alternatively, the image capture instrument may be afiber-optic bundle, such as a fiberscope, that couples to the imagingsystem. The image capture instrument may be single or multi-spectral,for example capturing image data in the visible spectrum, or capturingimage data in the visible and infrared or ultraviolet spectrums.

The flexible catheter body 216 may also house cables, linkages, or othersteering controls (not shown) that extend between the instrument body204 and the distal end 218 to controllably bend or turn the distal end218 as shown for example by the dotted line versions of the distal end.In embodiments in which the instrument system 200 is actuated by arobotic assembly, the instrument body 204 may include drive inputs thatcouple to motorized drive elements of the robotic assembly. Inembodiments in which the instrument system 200 is manually operated, theinstrument body 204 may include gripping features, manual actuators, andother components for manually controlling the motion of the instrumentsystem. The catheter system may be steerable or, alternatively, may benon-steerable with no integrated mechanism for operator control of theinstrument bending. Also or alternatively, the flexible body 216 candefine one or more lumens through which interventional instruments canbe deployed and used at a target surgical location.

In various embodiments, the interventional instrument system 200 mayinclude a flexible bronchial instrument, such as a bronchoscope orbronchial catheter for use in examination, diagnosis, biopsy, ortreatment of a lung. The system is also suited for navigation andtreatment of other tissues, via natural or surgically created connectedpassageways, in any of a variety of anatomical systems including thecolon, the intestines, the kidneys, the brain, the heart, thecirculatory system, or the like.

When using an interventional instrument system 200 to conduct aprocedure within a patient it may be desirable for the surgeon to havesimultaneous access to various forms of data related to the procedure,as described herein. For instance, when guiding an interventionalinstrument through certain portions of the anatomy such as therespiratory system, an endoscope may be too large to fit safely throughthe anatomy alongside the interventional instrument system 200. In suchprocedures, the surgeon may wish to supplement or replace the display ofan endoscopic camera with the display of preoperative or intraoperativeimages of the type described above. Additionally, the surgeon may wishto supplement the display of an endoscopic camera with the display of anoverview representation of the anatomy indicating the location of theinterventional instrument relative to the procedure site or a particulartarget location within the anatomy.

FIG. 3 illustrates a method 300 for generating a dynamic display of athree dimensional volumetric representation of anatomic passageways in adeformed state. At 302, a three dimensional volumetric representation(i.e., a solid model) of anatomic passageways of a patient anatomy isreceived or created from preoperatively or intra-operatively generatedimages using technology such as computerized tomography (CT), magneticresonance imaging (MRI), fluoroscopy, thermography, ultrasound, opticalcoherence tomography (OCT), thermal imaging, impedance imaging, laserimaging, nanotube X-ray imaging, or the like. FIG. 4 illustrates atleast a portion of a three dimensional volumetric representation 400 ofpatient anatomic passageways as received or created at step 302 of themethod 300. The three dimensional volumetric representation 400represents the various lung passageways 402 in a reference state, suchas a full exhalation state of a patient's breathing cycle.

Referring again to FIG. 3, the method 300 further includes, at 304,creating a piece-wise rigid reference skeleton tree of nodes andlinkages from the reference model in the reference state. FIG. 5illustrates a skeleton tree 420 based on the three dimensionalvolumetric representation 400 and includes a plurality of nodes 422interconnected by linkages 424 to approximate the structure of the threedimensional volumetric representation 400. The nodes 402 of the skeletontree 420 may be located at bifurcations of the anatomic passageways, atpoints of significant bend or twist, and/or at any other point along theanatomic passageway. The nodes may be generally centered within theanatomic passageways, but in alternative embodiments may be locatedalong passageway walls or at other locations with respect to referencestructures of the anatomy. The linkages 424 are straight segments thatextend between the nodes. The linkages are generally centered within theanatomic passageways, but in alternative embodiments may be locatedalong passageway walls or at other locations with respect to referencestructures of the anatomy.

Referring again to FIG. 3, the method 300 further includes, at 306,creating a reference geometric model. In one embodiment, as shown inFIG. 6, the geometric model 450 is a polygon mesh model comprised of aplurality of triangles 452 representing the a surface (interior orexterior) of the anatomic passageways. For example, a mesh model for aportion of an anatomic passageway may include approximately 130,000triangles. In alternative embodiments, the polygon mesh model maycomprise quadrilaterals or other flat, convex, or concave polygons. Eachvertex of mesh model 450 may be bound to one of the nodes 422 theskeleton tree 420. Thus, each vertex of the mesh model 450 bound to aselected node 422 is also bound to the skeleton linkages 424 connectedto that selected node.

Referring again to FIG. 3, the method 300 further includes, at 308,measuring at least one deformation of the anatomic passageways due toanatomical motion. Many regions of the patient anatomy are dynamic innormal function (e.g., heart, lungs, kidneys, liver, blood vessels). Inthis embodiment, the anatomical motion may be cyclical anatomical motionof the lungs caused by, for example, respiration or the cardiac cycle.The deformation is measured in at least one state of the anatomic cycledifferent from the state of the reference state. For example, if thereference state for the respiration cycle is full exhalation, thedeformed state may be at a state of full inhalation. Additionally oralternatively, the deformed state may occur at a state between fullinhalation and full exhalation. If the anatomic motion includes motiondue to the cardiac cycle, the reference state may be, for example, theearly diastole state and the deformed state may be another phase of thecardiac cycle such as atrial systole, isovolumic ventricularcontraction, ventricular ejection, or isovolumic ventricular relaxationstates. The deformation of the anatomic passageways may be determinedfrom preoperative or intra-operative images using any of the previouslydescribed imaging technologies, from shape sensor measurements, fromposition sensor measurements, or other known methods of measuringdeformation due to motion.

At 310, the method 300 includes measuring deformation of the anatomicpassageways due to forces applied by an interventional instrument (e.g.,catheter 202) positioned internal to the passageways. The shape of theinterventional instrument may be sensed using any of the above describedmethods for instrument shape sensing, including, for example the use ofan optical shape sensing fiber.

At 312, the method 300 includes creating a skeleton tree deformed by theinfluence of the anatomical motion and the interventional instrument.FIG. 7 illustrates a skeleton tree 460 of the anatomic passageways in adeformed state due to anatomic motion. In this illustration, the lungpassageways are in the deformed state of full inspiration. In thedeformed skeleton 460, the position of the nodes 422 and the positionand orientation of the linkages 424 are modified to align with theanatomic passageways from the imaged anatomy in the deformed state. FIG.8 illustrates a skeleton tree 470 of the anatomic passageways in thereference state of expiration but in a deformed state due to forcesapplied by an interventional instrument 472 within some of the anatomicpassageways. In the deformed skeleton 470, the position of the nodes 422and the position and orientation of the linkages 424 are modified basedon the shape measurements for the interventional instrument 472. Theshape of the interventional instrument 472 may directly deform thepassageways in which the interventional instrument is located but mayalso indirectly deform the adjacent passageways due to forces applied tothe tissue connecting the passageways. FIG. 9 illustrates a skeletontree 480 of the anatomic passageways in a deformed state due to thecombination of anatomic motion (e.g., full inspiration FIG. 7) andforces applied by the interventional instrument (e.g., FIG. 8). Invarious alternative embodiments, deformations of the anatomicalpassageways caused by other forces may be measured and used to createthe composite deformed skeleton tree.

Referring again to FIG. 3, the method 300 further includes, at 314,creating a deformation field to describe the measured deformations dueto anatomical motion and/or interventional instrument forces. Forexample, the deformation field may include a three dimensional fieldvector array describing the deformation of the anatomical passagewaysfrom the full exhalation reference state to the full inhalationdeformation state with a sequence of intermediate deformation statesbetween the reference state and the full deformation state. Asillustrated in FIG. 10, a deformation field 490 may include a threedimensional field vector array describing the three dimensionaldeformation of skeleton tree 420 into the skeleton tree 480.

Referring again to FIG. 3, the method 300 further includes, at 316,applying the deformation field to the reference geometric model tocreate a deformed geometric model. Generally, for each vertex in thereference mesh model 450, an interpolation of the deformation field 490is performed at each time t. Each vertex from the reference mesh model450 is then transformed into a corresponding vertex of a deformed meshmodel 500 (FIG. 11).

Linear blend skinning (LBS) techniques, known to those of skill in theart, may be used in the creation of the deformed mesh model. With LBStechniques, each vertex of each triangle 452 of the mesh model 450 isbound to the skeleton tree 420 which is responsible for deforming thevertex. In LBS terminology, the linkages of the skeleton are consideredthe “bones” and provides the “bone influences.” Each vertex may also beassigned a weight (w_(i)) for each linkage in the skeleton thatinfluences the vertex. The weighting assignments are such that for eachweight, 0≦w_(i)≦1 and Σ w_(i)=1. The weights may be found experimentallyby creating different skeleton poses and then changing the weights untilthe mesh deforms accordingly. To deform each vertex (v) from its initialpose in the mesh model 450, a weighted combination of the vertexdeformed by the skeleton linkages is used:

Deformation  Formula:$v_{deformed} = {\sum\limits_{i = 1}^{N}{w_{i}^{*}M_{i}^{*}v_{initial}}}$

where N is the number of bone influences, i is a link in the skeletonand M is an absolute link transform matrix, such as the deformationfield 490, which describes the skeletal deformation.

An example method for determining the weightings is provided. With twolinkage influences (i.e., bone influences) for a selected vertex v ofthe mesh, N=2 in the deformation formula. To determine w₁ and w₂ for thevertex v, the two closest links to v are chosen. The first closest linkis l₁ and the second closest link is l₂. The distance between v andl₁(l₂) is d_(v),l₁ (d_(v),l₂), defined as the shortest Euclideandistance between v and a point of l₁(l₂).

To compute d_(v),l₁ and d_(v),l₂, the dot product of vectors is appliedto test whether the shortest distance between a point P (at the vertexv) and a segment S (i.e., a linkage of the

skeleton) is between P and one of the endpoints of S. This testing isdescribed as follows:

The algorithm may also be represented as:

distance( Point P, Segment P0:P1 ) { v = P1 − P0 w = P − P0 if ( (c1 =w·v) <= 0 ) return d(P, P0) if ( (c2 = v·v) <= c1 ) return d(P, P1) b =c1 / c2 Pb = P0 + bv return d(P, Pb) }

Thus, w₁ and w₂ can be computed as the normalization of d_(v),l₁ andd_(v),l₂:

$w_{1} = \frac{d_{v,l_{1}}}{d_{v,l_{1}} + d_{v,l_{2}}}$$w_{2} = \frac{d_{v,l_{2}}}{d_{v,l_{1}} + d_{v,l_{2}}}$

Thus, the weightings for each vertex of the mesh can be determined andeach deformed vertex (v_(deformed)) in the mesh may be determined. Animplementation of the mesh model deformation using a graphics processingunit (GPU) is provided at FIG. 14.

Referring again to FIG. 3, the method 300 further includes, at 318,deforming the reference three dimensional volumetric representation 400into alignment with the deformed mesh to generate an image of thedeformed three dimensional volumetric representation 510 as shown inFIG. 12.

At 320, a composite image 520 (FIG. 13) is generated displaying thedeformed three dimensional volumetric representation 510 or deformedmesh model 450 with an image of the interventional instrument 472.

To speed the creation of the deformed mesh model such that the deformedmodel may be dynamically displayed at an approximately real-time displayrate, a software and/or hardware based accelerator, such as a parallelcomputing platform that uses GPU, may be used. With such a computingplatform, the deformed images of the anatomic passageways, from thereference state to the full deformation state and including all of theintermediate deformation states may be displayed. The GPU may allowdisplay of the reference and deformed state images at a rate ofapproximately 30 different frames per second and in some embodiments ata rate of approximately 50 different frames per second.

FIG. 14 illustrates a method 600 of mesh model deformation [e.g., step316 of method 300] using a GPU 602. At 604, the mesh model in thereference state (e.g., mesh 450) is provided to a central processingunit (CPU) 606. A loader 608 running on the CPU 606 loads the mesh modelto a main memory (not shown). From the memory, the mesh model istransferred to the GPU 602.

A mapping phase 610 is also performed on the CPU. FIG. 15 illustrates amapping technique for mapping between the mesh space 630 (e.g., aportion of the mesh model 450) to a 3D texture space 632 that is storedin 3D texture memory 612. The 3D texture memory 612 on the GPU 602stores a rigid transform for each node of the skeleton tree and forinterpolated coordinates between the skeleton nodes. The 3D texturememory provides a fast and convenient format for storing the rigidtransforms for the skeleton nodes and for interpolating transforms forcoordinates in between the nodes. The speed of the interpolation allowsfor the transformation and movement of the mesh model bound to theskeleton model in approximately real time. The use of rigid transformsover many constituent nodes of the skeleton approximates a non-rigidtransform over the entire mesh model space. Each (T_(x), T_(y), T_(z))texture space coordinate in a 3D texture memory space 632, is mapped toa corresponding mesh space coordinate (M_(x), M_(y), M_(z)) in the meshmodel space 630. For (M_(x), M_(y), M_(z)), closest links l₁(l₂) andweightings w₁(w₂) are determined as described above for the LBStechnique. If (M_(x), M_(y), M_(z)) is too far from any link of theskeleton, than w₁=w₂=0. To save the memory space, the output of themapping phase 610 is a mapping table (shown below) with 5 columns if andonly if w₁≠0.

(T_(x), T_(y), T_(z)) Index of l₁ w₁ Index of l₂ w₂The mapping table may only need to be computed once for eachdeformation. The mapping table is moved to the GPU 602.

For each time t, a non-rigid transform 614 is moved to the GPU 602. Thenon-rigid transform algorithm 614 is used to compute a rigid transformfor each node of the skeleton tree 420 to describe how that node shouldmove based on the deformed skeleton tree 480. At 616, the non-rigidtransform 614 is used by the GPU 602 to compute a transform for eachnode in the skeleton tree. Based on the created mapping table, a fulldeformation field is developed, from the transformed skeleton treenodes, for each interpolated coordinate in the 3D texture space 632. The3D texture memory 612 stores the transforms for each coordinate in the3D texture space 632. The fields of the 3D texture memory 612 are filledsimultaneously by the GPU. Separate threads (i.e., small sequences ofindependently managed programmed instructions) of the GPU work tocompute a deformation value, using the Deformation Formula providedabove, for each coordinate of the 3D texture memory. The 3D texturememory in the GPU serves two purposes. First, the dimensions of thetexture are much smaller than the model space. For example, the 3Dtexture memory may use a 128×128×128 voxel array and the model space mayuse a 1024×1024×1024 voxel array. Second, fetching the value in the 3Dtexture memory of the GPU with linear interpolation is very fast.

At 618, with one thread working on each vertex of the mesh model 450, athread fetches a value (using the mapping table) from the 3D texturememory 612 that corresponds to the position of the vertex in the initialmesh model 450 and transforms it into a deformed vertex. At 620, with adeformed vertex created for each of the reference state vertices, adeformed mesh model is generated and displayed. The display of thedeformed mesh model may be presented dynamically with the display of thedeforming mesh model updated at a high display rate corresponding to thenear real-time deformation of the patient anatomy. For example, the rateof display may be approximately 30 or more frames per second. Thus, aclinician navigating an interventional instrument through the patientanatomy is provided with a current image of the patient anatomy in itscurrent state of deformation.

One or more elements in embodiments of the invention may be implementedin software to execute on a processor of a computer system such ascontrol system 112. When implemented in software, the elements of theembodiments of the invention are essentially the code segments toperform the necessary tasks. The program or code segments can be storedin a processor readable storage medium or device that may have beendownloaded by way of a computer data signal embodied in a carrier waveover a transmission medium or a communication link. The processorreadable storage device may include any medium that can storeinformation including an optical medium, semiconductor medium, andmagnetic medium. Processor readable storage device examples include anelectronic circuit; a semiconductor device, a semiconductor memorydevice, a read only memory (ROM), a flash memory, an erasableprogrammable read only memory (EPROM); a floppy diskette, a CD-ROM, anoptical disk, a hard disk, or other storage device, The code segmentsmay be downloaded via computer networks such as the Internet, intranet,etc.

Note that the processes and displays presented may not inherently berelated to any particular computer or other apparatus. The requiredstructure for a variety of these systems will appear as elements in theclaims. In addition, the embodiments of the invention are not describedwith reference to any particular programming language. It will beappreciated that a variety of programming languages may be used toimplement the teachings of the invention as described herein.

While certain exemplary embodiments of the invention have been describedand shown in the accompanying drawings, it is to be understood that suchembodiments are merely illustrative of and not restrictive on the broadinvention, and that the embodiments of the invention not be limited tothe specific constructions and arrangements shown and described, sincevarious other modifications may occur to those ordinarily skilled in theart.

What is claimed is:
 1. A method comprising: receiving a reference threedimensional model of a branched anatomical formation in a referencestate; applying a three dimensional deformation field to the referencethree dimensional model to create a deformed three dimensional model ofa deformed state of the branched anatomical formation; and dynamicallydisplaying an image of the deformed three dimensional model of thedeformed state of the branched anatomical formation.
 2. The method ofclaim 1 wherein applying the three dimensional deformation field to thereference three dimensional model includes interpolating the threedimensional deformation field for a point on the reference threedimensional model.
 3. The method of claim 2 wherein applying the threedimensional deformation field to the reference three dimensional modelfurther includes transforming the point on the reference threedimensional model to a point on the deformed three dimensional model ofthe deformed state of the branched anatomical formation.
 4. The methodof claim 1 wherein applying the three dimensional deformation field tothe reference three dimensional model is performed on a graphicalprocessing unit.
 5. The method of claim 1 wherein the deformed state ofthe branched anatomical formation is caused, at least in part, by aperiodic anatomical motion.
 6. The method of claim 1 wherein thedeformed state of the branched anatomical formation is caused, at leastin part, by an interventional instrument positioned within the branchedanatomical formation.
 7. The method of claim 6 further comprising:displaying a composite image including an image of the interventionalinstrument positioned within the branched anatomical formation and theimage of the deformed three dimensional model of the deformed state ofthe branched anatomical formation.
 8. The method of claim 1 whereinreceiving the reference three dimensional model includes receiving athree dimensional mesh model.
 9. The method of claim 1 wherein thedeformed three dimensional model includes a deformed three dimensionalmesh model.
 10. The method of claim 9 wherein applying the threedimensional deformation field to the reference three dimensional modelto create a deformed three dimensional model of a deformed state of thebranched anatomical formation includes creating a deformed set ofvertices, wherein the deformed three dimensional mesh model comprisesthe deformed set of vertices.
 11. The method of claim 1 furthercomprising generating the three dimensional deformation field bygenerating a reference skeletal tree for the reference state of thebranched anatomical formation; generating a deformed skeletal tree forthe deformed state of the branched anatomical formation; and generatinga three dimensional array of field vectors describing a deformation fromthe reference state to the deformed state, wherein the three dimensionaldeformation field comprises the three dimensional array of fieldvectors.
 12. The method of claim 1 wherein displaying the image of thedeformed three dimensional model of the deformed state of the branchedanatomical formation includes displaying a sequence of images ofintermediate deformations of the branched anatomical formation at a rateof at least approximately 30 sequential deformation images per second.13. A processing system comprising: a processor; and a memory havingcomputer readable instructions stored thereon, the computer readableinstructions, when executed by the processor, cause the system to:receive a reference three dimensional model of a branched anatomicalformation in a reference state; apply a three dimensional deformationfield to the reference three dimensional model to create a deformedthree dimensional model of a deformed state of the branched anatomicalformation; and dynamically display an image of the deformed threedimensional model of the deformed state of the branched anatomicalformation.
 14. The processing system of claim 13 wherein applying thethree dimensional deformation field to the reference three dimensionalmodel includes interpolating the three dimensional deformation field fora point on the reference three dimensional model.
 15. The processingsystem of claim 14 wherein applying the three dimensional deformationfield to the reference three dimensional model further includestransforming the point on the reference three dimensional model to apoint on the deformed three dimensional model of the deformed state ofthe branched anatomical formation.
 16. The processing system of claim 13wherein applying the three dimensional deformation field to thereference three dimensional model is performed on a graphical processingunit.
 17. The processing system of claim 13 wherein the deformed stateof the branched anatomical formation is caused, at least in part, by aperiodic anatomical motion.
 18. The processing system of claim 13wherein the deformed state of the branched anatomical formation iscaused, at least in part, by an interventional instrument positionedwithin the branched anatomical formation.
 19. The processing system ofclaim 18 further comprising: displaying a composite image including animage of the interventional instrument positioned within the branchedanatomical formation and the image of the deformed three dimensionalmodel of the deformed state of the branched anatomical formation. 20.The processing system of claim 13 wherein receiving the reference threedimensional model includes receiving a three dimensional mesh model. 21.The processing system of claim 13 wherein the deformed three dimensionalmodel includes a deformed three dimensional mesh model.
 22. Theprocessing system of claim 21 wherein applying the three dimensionaldeformation field to the reference three dimensional model to create adeformed three dimensional model of a deformed state of the branchedanatomical formation includes creating a deformed set of vertices,wherein the deformed three dimensional mesh model comprises the deformedset of vertices.
 23. The processing system of claim 13 wherein thecomputer readable instructions, when executed by the processor furthercause the system to generate the three dimensional deformation field bygenerating a reference skeletal tree for the reference state of thebranched anatomical formation; generating a deformed skeletal tree forthe deformed state of the branched anatomical formation; and generatinga three dimensional array of field vectors describing a deformation fromthe reference state to the deformed state, wherein the three dimensionaldeformation field comprises the three dimensional array of fieldvectors.
 24. The processing system of claim 13 wherein displaying theimage of the deformed three dimensional model of the deformed state ofthe branched anatomical formation includes displaying a sequence ofimages of intermediate deformations of the branched anatomical formationat a rate of at least approximately 30 sequential deformation images persecond.